This invention relates generally to image producing machines, and more particularly to such a machine having a plurality of image pre-transfer substrate heating assemblies. Such assemblies are particularly useful in a high-speed phase change ink image producing machine or printer.
In general, phase change ink image producing machines or printers employ phase change inks that are in the solid phase at ambient temperature, but exist in the molten or melted liquid phase (and can be ejected as drops or jets) at the elevated operating temperature of the machine or printer. At such an elevated operating temperature, droplets or jets of the molten or liquid phase change ink are ejected from a printhead device of the printer onto a printing media. Such ejection can be directly onto a final image receiving substrate, or indirectly onto an imaging member before transfer from it to the final image receiving media. In any case, when the ink droplets contact the surface of the printing media, they quickly solidify to create an image in the form of a predetermined pattern of solidified ink drops.
An example of such a phase change ink image producing machine or printer, and the process for producing images therewith onto image receiving sheets is disclosed in U.S. Pat. No. 5,372,852 issued Dec. 13, 1994 to Titterington et al. As disclosed therein, the phase change ink printing process includes raising the temperature of a solid form of the phase change ink so as to melt it and form a molten liquid phase change ink. It also includes applying droplets of the phase change ink in a liquid form onto an imaging surface in a pattern using a device such as an ink jet printhead. The process then includes solidifying the phase change ink droplets on the imaging surface, transferring them the image receiving substrate, and fixing the phase change ink to the substrate.
It has been found that relatively effective image transfer in an ordinary speed (12–32 copies per minute) solid ink printer can be achieved from having the substrate pre-heated or heated prior to image transfer. Conventionally, as disclosed for example in U.S. application Ser. No. 10/320,821, a single stage pre-heater has been used to transfer heat to the substrate prior to the substrate being registered for image transfer. Unfortunately, it has been found that in relatively high speed (40 and more copies per minute) solid ink printers, for example, a single stage heater is tends to transfer insufficient heat or too much heat to the substrate. This is because such machines or printers call for substrates to be transported at the high substrate transport speeds (approximately 1440 mm/sec). This problem is made even worse where the substrate transport speeds are varied between a slow speed and an accelerated.
There is therefore a need for a pre-transfer substrate heating arrangement that is capable of providing just enough heat to substrates at relatively high speed for achieving effective image transfer in a solid ink image producing machine or printer.
In accordance with the present disclosure, there is provided an ink image producing machine that has (a) imaging devices, including at least one ink jet print head and an image receiving station for producing an ink image on a heated substrate; (b) a substrate handling assembly including holding devices for holding supplies of substrates, and transport feeding devices for transporting and feeding substrates in a substrate direction towards the image receiving station; (c) a first substrate heating assembly located upstream of the image receiving station for initially heating each substrate being fed and transported from the holding devices; and (d) a second substrate heating assembly located downstream of the first substrate heating assembly and upstream of said image receiving station, relative to the substrate feeding direction, for controllably re-heating each substrate, initially heated by the first substrate heating assembly, to a desired ink image receiving temperature.